Answer to "mid-2010 iMac 27" best way to add SSD to make fusion drive"I just did the same thing to a mid-2010 27' Mac (2390). I replaced the optical drive as I rarely use it, I bought a caddy which comes with an external USB enclosure for the DVD drive: http://www.amazon.co.uk/caddy-MacBook-replaces-SuperDrive-enclosure/dp/B00A2VNUK4 I'm not sure about which method is better, but now if I ever wanted to I could still add another (3rd) internal drive to the free SATA port on the back of the motherboard. For SSD I bought a 500GB Crucial BX100 which I "fusion drived" with the original 2TB Seagate. While I was at it I got a second hand i7-870 processor and replaced my original i3-550. iMac Intel Core i3 CPUからCore i7にアップグレードする Updated all my apps (system and rest) to latest. Very pleased with all the upgrades, my mac feels so fast ;-) And with the excellent tutorials from fixit and others, it wasn't that hard. Only an hour work.